In a number of electronic applications, for example, power supplies and safety systems, it is necessary to exchange data between circuits that are electrically isolated from each other. For example, in an air-bag deployment controller, two control domains work in parallel to deliver a validation signal to fire the air-bag. To minimize fault coupling between these control domains, each domain has independent clock sources and power supplies. Furthermore, portions of an airbag controller are isolated from other portions of a car's electronic system in order to ensure that the airbag can be deployed even in the event of a failure of the car's electronic system. In some systems, communication takes place across an isolation barrier such as an air gap, printed circuit board (PCB), or other isolating material that does not pass direct current (DC). In some systems, communication takes place between circuits that are not referenced to the same ground potential.
Conventional systems for data exchange over isolation barriers include, for example, optocouplers, capacitive couplers, and/or inductive couplers, which transmit energy across the isolation barrier. An LED of an optocoupler transmits optical power to drive an active data level, while inductive and capacitive couplers transmit repetitive current and/or voltage pulses to be detected by an isolated receiver. A transmitter for an inductive coupler, for example, generally sends data by passing current pulses though a coil and or a transformer. A capacitive coupler based on a charge pump principal, on the other hand, sends current pulses by transferring charge from at least one capacitive storage element at the transmitting side to an isolated receiving element at the receiving side. Because isolation barriers generally do not pass DC current, even the transmission of static data usually requires continual transmission energy in the form of refresh pulses in order to prevent data failures.
What is needed are reliable and power efficient systems and methods for transferring data across an isolation barrier.